1. Field of the Invention
The present invention relates to a correction arithmetic circuit and a signal processor.
2. Description of Related Art
In order to increase detection accuracy of a sensor, it is necessary to appropriately correct a sensor output characteristic that varies with temperature. For example, assume a case of correcting the sensor output characteristic at 60° C. with the sensor output characteristic at 20° C. used as a reference. In this case, an approximate formula representing the sensor output characteristic at 60° C. (a sensor output variation amount from the 20° C. reference) may be prepared beforehand, and a correction amount for correcting the sensor output may be calculated by using the approximate formula. When it is necessary to correct the sensor output characteristic at another temperature, another approximate formula may be prepared for the temperature in the same manner as above.
In regard to a signal processor that performs various signal processing functions synchronizing with a reference clock signal, in order to increase output accuracy of such a signal processor, it is desirable to prepare, as a clock signal generator, an oscillator having as small a frequency temperature characteristic as possible (that is, an oscillator whose oscillation frequency is not liable to vary with the ambient temperature).
Some examples of prior arts related to the above are disclosed in Japanese Patent Application Publications No. 2004-125685, 2009-032142, and 2004-120353.
However, in a case of a sensor having a wide range of operation temperature (for example, −40° C. through 140° C.), it is unrealistic from a viewpoint of circuit scale (memory capacity for storing coefficients of approximate formulae) to prepare an approximate formula for each temperature.
Moreover, the high price of highly accurate oscillators limits application to which such highly accurate oscillators are applicable. Conventionally, measures have been taken at the time of design such that resistor elements each having a positive or negative temperature characteristic, etc. are combined to thereby cancel a frequency temperature characteristic of an oscillator, but with such measures taken at the time of design, it is difficult to perform adjustment suitable for temperature characteristics of actual circuits.